Conventionally, the cardiac resynchronization therapy (CRT) has been known as an example of heart failure treatment. This therapy is used for treatment of a disease in which abnormality of the impulse conduction system of the heart leads to a wrong timing of motion of the cardiac muscle surrounding a ventricle, so that core-walls of the right and left ventricles do not move at the same time, and the ventricles do not contract at the correct timing, thus causing insufficient cardiac output of the blood, for example.
In the CRT, an electrode is placed in the part where the heart hardly moves (the site of latest activation) so that the ventricles of the heart contract in a synchronized manner. Specifically, in the CRT, the site of latest activation is determined through strain analysis by using an ultrasound diagnosis apparatus, and the electrode is placed on the closest vein to the site of latest activation with reference to the X-ray image radiographed by an X-ray diagnosis apparatus.
The electrode placed as described above applies stimuli electric potential at a proper timing, whereby the cardiac muscle contracts at a proper timing and controls the motion of the ventricles. In the conventional technology, however, a superimposed image of an X-ray image and another medical image can be hardly displayed with high visibility.